Here's my understanding (and also what I am able to do): Opening up in 6 directions... front-back, up-down, side-side... and actually in all directions (so, infinite diagonals in between those 6 main points) creates a sphere (a structural "force field"), of which you are the center. It creates a very powerful stability in you and, coupled with the maintaining of an arcing body structure to direct and re-direct force to an from the ground, it creates what the Chinese internal arts call "Peng jing," the primary force used to power waza. Peng power is the core power of aiki-age and aiki-sage... manifestations of Peng (dunno any Japanese term for it) that involve rolling that invisible sphere in the direction you want uke's body to go. Or bouncing him off... or spinning him off tangentially (he feels his force moving away, as though on the surface of a spinning ball). Now you can add the spirals... and that's where silk-reeling comes in.

Silk-reeling is not the 6 directions or Peng; however, it works hand-in-hand with Peng, and also you're always working the 6 directions to maintain your structure, and in that regard when you are silk-reeling you are expressing the 6 directions. But the reeling itself is a specific thing -- setting in motion a constant In-Yo/Yin-Yang trade of opposing forces using a figure-eight type of movement from your kuas, combined with actions initiated from the feet and legs. This is the source of huge power which can be used to move uke irresistibly into a throw, or to power ate-waza, strikes and kicks. An experienced practitioner can do this without looking like they are overtly moving -- you won't see their hips or legs move, or just tiny, minute "twitches" maybe. The movements are so small and refined that they are generating great power with minimal motion in nage... but the effect it will have on uke will be magnified.

When you see someone do aiki-age on uke, then throw him off to the side, it's an exercise using Peng, and silk-reeling power. First, Peng to capture and unseat uke's center, then reeling him off into the throw.